The present invention relates to low insertion force mating male and female electrical contact structures and to electrical connectors incorporating them. More particularly, it relates to a low insertion force contact structure including a male terminal having a twisted lead-in portion with at least one surface adapted to engage at least one contact of a female terminal which is effective to gradually deflect the contact portion of the female from an initial position to a final mated position during insertion to provide a lower overall insertion force.
Various single and dual spring arm female contact electrical terminals have been provided in the past for making electrical contact with male terminals such as pins, blades, edge card contact pads and the like. Generally, in these arrangements, the male terminal must be inserted into the female with sufficient force to overcome the resistance to insertion presented by the female terminal. The insertion force of the contact structure includes a lifting component which represents the force required to lift or spread the female contact portions apart to permit passage of the male terminal into the female and also a horizontal frictional component provided as the female contact portions wipe against the male terminal during the insertion.
In multicircuit arrangements including a large number of female terminals mounted in a connector adapted to mate with a male connector including a correspondingly large number of male terminals, the individual insertion forces associated with each pair of contacts combine so that the overall insertion force required to mate the male and female connectors can be extremely large.
Earlier efforts to provide an electrical contact structure characterized by reduced insertion force have generally included modifying the female terminal contacts. In U.S. Pat. No. 4,175,821, for example, a female terminal is disclosed including a dual opposed spring arm contact member wherein the contact portions of the opposed arms are axially offset from one another in the longitudinal direction. As the pin contact is inserted between the female spring arms, the pin engages the first spring arm on the female and lifts it out of the way, before contacting the second spring arm and moving that contact out of the way. A lower peak insertion force is provided by the arrangement because the lifting force needed to deflect the female to a final mated position is broken down into two smaller lifting steps, lifting one spring arm at a time during the insertion stroke instead of two at a time. The design described in the patent has several shortcomings. For example, the female terminal is adapted to receive a conventional square pin male terminal which includes a relatively short, chamfered tip portion. The tip portion of the male terminal typically is a rough machined surface which wipes against the precious metal plated contact portion on the female. Repeated mating results in abraided contacts which tends to make the contact arrangement electrically unreliable in prolonged use. Increasing the precious metal plating in the contact area results in increased cost which is also undesireable.
Another modified low insertion force female terminal is disclosed in U.S. Pat. No. 4,607,907. The female contact in this patent is a stamped and formed terminal including a rearward box member from which extend cantilevered spring arms including contact portions at their free ends. The contact portions are axially longitudinally offset as were the contact portions in the aforementioned patent, but in addition, they are configured so that they overshoot the midline of the insertion region which permits lower spring rates to be used. The female contact further includes horizontal spacing between the cantilevered spring arms so that the contact portions are horizontally spaced one from the other. This permits the contact portions to be plated with precious metals in a lower cost process. This female contact provides a lower peak insertion force for the same reasons, i.e. the male lifts one cantilevered spring arm at a time during insertion. The overshot design of the contact portions permits lower spring rates in the spring members to be used, so that the stiffness of each spring member is reduced and the force required to lift each spring arm contact during pin insertion is reduced.
This design also possesses several shortcomings. As with the first mentioned female, the rough cut abrasive edge of the chamfered lead-in on the male pin scrapes against the precious metal coated contact portions of the spring arms during pin insertion. Long term electrical reliability in repeated mating operations is generally not obtained. The female terminal is stamped and then formed in a manner which produces a significantly large amount of wasted sheet metal stock. Furthermore, because these female terminals are formed after stamping to provide the box portion and opposed spring arm structure, they cannot be provided on a carrier strip spaced apart by centerline spacings adapted for ready insertion in a connector housing in a single stamping operation. Instead, after they are formed, they must be repositioned to a spacing appropriate for insertion into a housing. This requires additional manufacturing and assembly steps in use.
A new approach to providing a low insertion force contact is disclosed in copending U.S. application Ser. No. 912,887, filed Sept. 26, 1986. The mating electrical contact structure described therein includes an electrically conductive elongated tubular female receptacle adapted to receive a mating male contact. The male contact has at least one resilient elongated beam. Either the female tubular receptacle or the male terminal includes a predefined longitudinally extending rotational skew or twist profile. As the male terminal is inserted into the female receptacle, the resilient beam on the male terminal is progressively deflected along the predefined rotational skew. In accordance with the design, the rotational deflection provides a torque which generates the mated contact force between the male and female contacts. The degree of the rotational skew in this contact arrangement determines the amount of progressive deflection during insertion.
The proposed design also has some shortcomings. The male terminal member in at least one embodiment must be assembled and the additional assembly steps add to the cost of the contact structure. Another disadvantage in manufacturing is encountered because the interior of the tubular female member is extremely difficult to plate with precious metals satisfactorily after it is formed. The opposed inner surfaces will create field effect interference in plating operations, resulting in poor or lower quality plating. Moreover, the contact design structure is very sensitive to misalignment of the mating female and male terminals. If the male terminal member is positioned to be slightly offset from the central axis of the tubular female, the low insertion force characteristics can be changed into very high insertion forces because a misalignment will tend to deflect or try to deflect nonresilient members in the system.